Month ago had a misfire on my vehicle Lincoln Town Car so I use a scanner and had a code which said cyclinder 2 misfire so I took it to my Mechainc and he replace just 1 coil and 1 spark plug the rest was not replace my Mechainc said you don't need to replace them til it fails. Car ran nicely after a month now my car as another problem check engine light on and blinking as well my car is running rough, jerking, and shaking when I acceralte. So I went and bought a bottle of Fuel & Exhaust system cleaner which is suppose to clean the Cataylic and 02 sensor to give a shot to see but no luck but it did help a little bit so I ran the scanner and it give me a code which say PO430 Cataylic system efficiency below threshold bank 2. Can you please tell me what is the cause of this problem is it the 02 sensor or Cataylic convertor or something else as I have no clue?

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The code is meant to indicate your catalytic converter is not performing up to par with the EPA (environmental protection agency) standards. Your car uses the oxygen sensors to monitor the catalytic converter (cat) efficiency. There is an O2 sensor before and after the cat. If the catalytic is working effectively, the O2 sensor after the catalyst will show much less HC’s (hydrocarbons) that at the front of the cat. If the cat is not performing as it should, the rear O2 will see close to the same amount of HC’s after the catalytic converter.

Most of the time this code requires the replacement of the catalytic converter. There are times when one or both of the O2 sensors that monitor the cat are bad. This can be determined by monitoring scan tool data for a reaction from the O2 when you snap the throttle. In addition, you can use an exhaust gas analyzer monitor the tail pipe emissions from a cold start up. The cat takes sometime to begin working on a cold start, so there should be a significant difference in tailpipe emissions once the cat warms up. Gas analyzers are very expensive, so it is unlikely most people will have access to one. If you need a definitive diagnosis, a certified professional from YourMechanic can come to your car’s location to pinpoint the cause of the code and proceed with repair.

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